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Date: Mon, 14 Sep 2020 11:38:29 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
To: Peter Xu <peterx@redhat.com>, Leon Romanovsky <leonro@nvidia.com>, Linus
 Torvalds <torvalds@linux-foundation.org>
CC: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>, "Maya B . Gokhale"
	<gokhale2@llnl.gov>, Yang Shi <yang.shi@linux.alibaba.com>, Marty Mcfadden
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	Christoph Hellwig <hch@lst.de>, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification
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On Fri, Aug 21, 2020 at 07:49:55PM -0400, Peter Xu wrote:
> From: Linus Torvalds <torvalds@linux-foundation.org>
> 
> How about we just make sure we're the only possible valid user fo the
> page before we bother to reuse it?
> 
> Simplify, simplify, simplify.
> 
> And get rid of the nasty serialization on the page lock at the same time.
> 
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> [peterx: add subject prefix]
> Signed-off-by: Peter Xu <peterx@redhat.com>
>  mm/memory.c | 59 +++++++++++++++--------------------------------------
>  1 file changed, 17 insertions(+), 42 deletions(-)

I don't have a detailed explanation right now, but this patch appears
to be causing a regression where RDMA subsystem tests fail. Tests
return to normal when this patch is reverted.

It kind of looks like the process is not seeing DMA'd data to a
pin_user_pages()?

Thanks,
Jason